This invention relates to an apparatus for catalytic conversion of hydrocarbon in the absence of added hydrogen or the consumption of hydrogen. More particularly, the present invention relates to a riser reactor for fluidized catalytic conversion.
The earlier fluidized catalytic cracking (FCC) process utilized a dense fluidized bed reactor in which fluid velocity was only 0.6-0.8 m/s, i.e. the weight hourly space velocity was only 2˜3, and the maximum fluid velocity was only 1.2 m/s, i.e. the weight hourly space velocity was only 5˜8. Product quantity and quality were adversely affected in the reactor because of the backmixing in the dense fluidized bed reactor. With the use of the zeolite catalyst having high activity and selectivity, a riser reactor was adopted to reduce fluid backmixing, and consequently, to improve the yield and quality of the desired product.
A riser reactor has made a great progress over a dense fluidized bed reactor as to geometric structure and operating mode, which are mainly embodied in that the initial feed and catalyst contacting at the bottom of the riser and the recovery of hydrocarbons from spent catalyst at the top of the riser are improved, and that the temperature gradient in the cross section of the riser and backmixing in vertical section of the riser have been reduced.
Techniques in initial feed and catalyst contacting tend to improve nozzle functions and to enhance the efficiency of initial feed and catalyst contacting. Improvement in nozzle functions tends to reduce pressure drop, to homogenize dispersion, to minimize the diameter of liquid droplets and homogenize liquid droplets distribution, which are disclosed in U.S. Pat. No. 4,434,049, U.S. Pat. No. 4,427,537, Chinese Patent No. 8801168 and European Patent No. 546,739. Techniques to enhance the efficiency of initial feed and catalyst contacting are disclosed in U.S. Pat. No. 4,717,467, U.S. Pat. No. 5,318,691, U.S. Pat. No. 4,650,566, U.S. Pat. No. 4,869,807, U.S. Pat. No. 5,154,818 and U.S. Pat. No. 5,139,748.
Another hot spot of research and development is to suppress overcracking and thermal reaction at the top of a riser. There are two technique routes at present, one is to use a rapid gas-solid separation apparatus at the outlet of the riser, which is disclosed in European Patent No. 162,978, European Patent No. 139,392, European Patent No. 564,678, U.S. Pat. No. 5,104,517, and U.S. Pat. No. 5,308,474, and the other is to use a quenching method in the outlet of the riser, which is disclosed in U.S. Pat. No. 5,089,235 and European Patent No. 593,823.
However, a conventional riser reactor is still an iso-diameter riser reactor. Fluid linear velocity is generally from about 4 m/s to about 5 m/s at the bottom of the riser. With the proceeding of cracking reaction and the decreasing of average molecular weight of hydrocarbons, fluid linear velocity is accelerated to 15˜18 m/s at the outlet of the riser. Fluid residence time is only 2˜3 seconds and thus some beneficial secondary reactions for the quality of desired products are suppressed in a conventional riser reactor. Therefore, it is necessary to modify the conventional riser reactor so as to favor the proceeding of the some secondary reactions and thus to obtain the desired products.
An object of the present invention is to provide a novel riser reactor, which not only can suitably increase secondary reaction time, but also can process plural hydrocarbon feedstocks.